As known, a rim for a bicycle wheel comprises an annular body intended to be coupled, on a radially outer side thereof, with a tyre of the bicycle wheel and, on a radially inner side thereof, with a plurality of spokes of the bicycle wheel.
Typically, the aforementioned annular body comprises opposite sidewalls and a bottom wall in which holes are formed for housing the heads of the aforementioned spokes.
On such sidewalls brake tracks are provided, on which the bicycle brake pads act.
In order to provide the rims made from light alloy (typically aluminium or alloys thereof) with a desired hardness, it is known to perform on such rims a surface treatment of plasma electrolytic oxidation (PEO).
However, outdoor tests have shown that the aforementioned treatment penalises the braking, making it discontinuous and/or irregular (in technical jargon, this is known as non-modular braking). In particular, such braking is initially very weak and then too sudden.
In order to make braking more continuous and/or regular, it is known to make suitably oriented grooves on the brake track.
EP 1 018 443 describes a rim comprising, at the brake track, a plurality of concentric circumferential grooves typically made in the extrusion step of the rim.
The Applicant has found that making the aforementioned grooves in the extrusion step requires that an extrusion matric is provided that is specially shaped to make such grooves, with a substantial economic burden and complication of the process. Moreover, after a lot of braking, the aforementioned concentric circumferential groves form corresponding groves on the brake pad and, when they reach a depth equal to the height of the grooves of the brake track, the brake pad no longer offers material to be abraded by the grooves of the brake track, this having a negative impact on the braking efficiency.
On the other hand, making concentric circumferential grooves through subsequent chip-removal mechanical machining would require either the use of a plurality of tools, one for each groove, or the use of a single tool and the consequent need to provide for a discontinuous relative radial movement between rim and tool. Also in this case there would be either an excessive economic burden or excessive complication of the process.
On the market there are also bicycle wheels comprising, at the brake track, a plurality of substantially parallel grooves oriented along a direction inclined by an angle close to 45° with respect to the circumferential or radial direction of the rim. Such rims are subjected to a plasma electrolytic oxidation surface treatment. Also in this case, making the plurality of grooves through subsequent chip-removal mechanical machining requires discontinuous relative circumferential movement between rim and tool, with consequent complication of the process.
Moreover, the Applicant has found that grooves of the type described above cause a lot of noise during braking.